The document discusses engineering challenges for extending the Purple Line subway under Los Angeles, including building tunnels through established areas, active fault zones, and groundwater. Key challenges include mitigating risks from earthquakes on two faults crossed by the alignment and addressing subsurface deposits of tar, gases, and oil. Tunnel construction involves large boring machines and lining tunnels to support them. Risks from liquefaction, gases, and tar sands will be mitigated through ventilation, detection systems, disposal, and structural design. The project began in 2014 and is the largest public works project in the nation.

1. Extension of Metro’sExtension of Metro’s
Purple LinePurple Line
Presented By:Presented By:
Eric ChristensonEric Christenson

2. Engineering Challenges andEngineering Challenges and
MitigationsMitigations
 Building a subway under a major cityBuilding a subway under a major city
that is already established.that is already established.
 Sustaining a tunnel through twoSustaining a tunnel through two
active fault zones.active fault zones.
 Most of construction is under theMost of construction is under the
ground water table.ground water table.
 Area has scattered natural depositsArea has scattered natural deposits
of tar, toxic gasses, and oil.of tar, toxic gasses, and oil.

4. First, Some Fun FactsFirst, Some Fun Facts
 Project started inProject started in
November 2014.November 2014.
 Largest public worksLargest public works
project and programproject and program
in the nation rightin the nation right
now.now.
 Already raised 1.2Already raised 1.2
billion for phase two.billion for phase two.
 To the right:To the right:
Hollywood andHollywood and
Highland station soHighland station so
far.far.

5. Construction of TunnelsConstruction of Tunnels
 Tunnels are 20’ inTunnels are 20’ in
diameter.diameter.
 They are parallelThey are parallel
and separatedand separated
about 20’ fromabout 20’ from
each other.each other.
 Varying depthsVarying depths
throughout projectthroughout project
from 50’ to 130’.from 50’ to 130’.

6. Tunnel Boring MachinesTunnel Boring Machines
 TBM’s are huge cylindricalTBM’s are huge cylindrical
machines that drill into themachines that drill into the
earth around 40’ per day.earth around 40’ per day.
 TBM’s on this project keepTBM’s on this project keep
pressure on the face and wallspressure on the face and walls
of the tunnel while installingof the tunnel while installing
tunnel liners to support thetunnel liners to support the
tunnel.tunnel.
 Different tunnel liners canDifferent tunnel liners can
accommodate specialaccommodate special
conditions.conditions.
 Under groundwater table thereUnder groundwater table there
will be secondary tunnel liners,will be secondary tunnel liners,
gaskets, and drainage systems.gaskets, and drainage systems.

7. Metro Tunnel DesignMetro Tunnel Design
 Metro design criteria uses two levels ofMetro design criteria uses two levels of
ground shaking hazard and fault offset:ground shaking hazard and fault offset:
the operating design earthquake (ODE),the operating design earthquake (ODE),
having a 50-percent probability ofhaving a 50-percent probability of
exceedance in 100 yearsexceedance in 100 years
 Maximum design earthquake (MDE),Maximum design earthquake (MDE),
having a 4-percent probability ofhaving a 4-percent probability of
exceedance in 100 yearsexceedance in 100 years
 Basically it is not feasible to design to lastBasically it is not feasible to design to last
over 100 years in this environment.over 100 years in this environment.

8. Through Two Active Fault Zones?Through Two Active Fault Zones?
 The tunnel alignment options in the CenturyThe tunnel alignment options in the Century
City/West Beverly Hills area cross two mappedCity/West Beverly Hills area cross two mapped
fault zones—the Santa Monica fault zone and thefault zones—the Santa Monica fault zone and the
West Beverly Hills Lineament (WBHL) fault zone.West Beverly Hills Lineament (WBHL) fault zone.
 Mitigate by minimizing area of tunnel thatMitigate by minimizing area of tunnel that
intersects faults.intersects faults.
 Make flexible tunnel liners and excavate a widerMake flexible tunnel liners and excavate a wider
tunnel by faults to allow for shear stress.tunnel by faults to allow for shear stress.

10. Exploration Plan Around Both Fault ZonesExploration Plan Around Both Fault Zones
 7 rotary-wash continuous core7 rotary-wash continuous core
boreholesboreholes
 49 hollow stem auger continuous49 hollow stem auger continuous
core boreholescore boreholes
 192 CPTs192 CPTs
 5 P-wave seismic reflection profiles5 P-wave seismic reflection profiles
 5 S-wave seismic reflection profiles5 S-wave seismic reflection profiles
 5 down hole suspension PS velocity5 down hole suspension PS velocity
measurementsmeasurements

11. Cannot Avoid FaultsCannot Avoid Faults
 The Santa Monica fault zone is capable ofThe Santa Monica fault zone is capable of
generating earthquakes in the magnitude rangegenerating earthquakes in the magnitude range
M6.9 to M7.2, with average surfaceM6.9 to M7.2, with average surface
displacements of approximately 3 to 6 feet.displacements of approximately 3 to 6 feet.
 A major event on the WBHL might be betweenA major event on the WBHL might be between
M6.4 (generally the lower end of the magnitudeM6.4 (generally the lower end of the magnitude
range for surface rupture) and M7.2, also withrange for surface rupture) and M7.2, also with
average surface displacements of up to 3 to 6average surface displacements of up to 3 to 6
feet, depending on the length of rupture on thefeet, depending on the length of rupture on the
northernmost portion of the Newport Inglewood-northernmost portion of the Newport Inglewood-
WBHL fault zone.WBHL fault zone.
 Designing for this maximum displacement wasDesigning for this maximum displacement was
not feasible, so the minimal cross sections arenot feasible, so the minimal cross sections are
crossing faults, repairs will be made when a faultcrossing faults, repairs will be made when a fault
ruptures.ruptures.

12. Liquefaction and SeismicLiquefaction and Seismic
SettlementSettlement
 Based on the magnitude of evaluatedBased on the magnitude of evaluated
liquefaction, a suitable mitigation will beliquefaction, a suitable mitigation will be
selected, either structural design, orselected, either structural design, or
ground improvement (such as deep soilground improvement (such as deep soil
mixing) or deep foundations to nonmixing) or deep foundations to non
liquefiable soil (such as drilled piles).liquefiable soil (such as drilled piles).
 Most of the project will be under the layersMost of the project will be under the layers
of threatening liquefaction so this does notof threatening liquefaction so this does not
pose a big threat.pose a big threat.

13. Hazardous Subsurface GasHazardous Subsurface Gas
OperationsOperations
 Measures will include the following forMeasures will include the following for
both tunnel and station operation:both tunnel and station operation:
 High volume ventilation systems withHigh volume ventilation systems with
back-up power sources.back-up power sources.
 Gas detection systems with alarms.Gas detection systems with alarms.
 Emergency ventilation triggered by theEmergency ventilation triggered by the
gas detection systems.gas detection systems.
 Automatic equipment shut-off.Automatic equipment shut-off.
 Maintenance and operations personnelMaintenance and operations personnel
trainingtraining

14. Tar Sand DisposalTar Sand Disposal
 Based on results, tar sands may alsoBased on results, tar sands may also
be transported to a facility wherebe transported to a facility where
they can be re-cycled andthey can be re-cycled and
incorporated into the asphaltincorporated into the asphalt
pavement manufacturing process.pavement manufacturing process.
 If not recyclable, they will go toIf not recyclable, they will go to anan
appropriate waste manifest to a localappropriate waste manifest to a local
landfill that accepts petroleum-landfill that accepts petroleum-
impacted soils.impacted soils.

17. Beverly Hills High SchoolBeverly Hills High School
 1. Tunneling can be safely carried out beneath the Beverly1. Tunneling can be safely carried out beneath the Beverly
Hills High School (BHHS) campus;Hills High School (BHHS) campus;
 2. Tunneling would not prevent future development of the2. Tunneling would not prevent future development of the
BHHS campus;BHHS campus;
 3. Tunneling would not impact the use of the BHHS campus3. Tunneling would not impact the use of the BHHS campus
as an emergency evacuation center;as an emergency evacuation center;
 4. Vibration and noise levels are within the FTA4. Vibration and noise levels are within the FTA
requirements and tunnel operation is not anticipated torequirements and tunnel operation is not anticipated to
have adverse impacts. The tunnel construction may causehave adverse impacts. The tunnel construction may cause
some low levels of noise and vibration for a day or two;some low levels of noise and vibration for a day or two;
 5. Tunneling can be constructed and operated safely in5. Tunneling can be constructed and operated safely in
gassy ground;gassy ground;
 6. Oil wells do not pose an unmitigable risk to tunneling.6. Oil wells do not pose an unmitigable risk to tunneling.
Should they be encountered, procedures will be in place forShould they be encountered, procedures will be in place for
their safe removal and reabandonment;their safe removal and reabandonment;

18. Beverly Hills High SchoolBeverly Hills High School
 7. In Century City, Constellation Boulevard is a viable7. In Century City, Constellation Boulevard is a viable
option for a station location, but Santa Monica Boulevard isoption for a station location, but Santa Monica Boulevard is
not due to unacceptable seismic risk;not due to unacceptable seismic risk;
 8. Tunneling through fault zones can be done safely;8. Tunneling through fault zones can be done safely;
 9. MTA's approach to risk management is correct;9. MTA's approach to risk management is correct;
 10. Further site investigations will be conducted and10. Further site investigations will be conducted and
measures will be implemented to reduce risks to levels thatmeasures will be implemented to reduce risks to levels that
are as low as reasonably practicable;are as low as reasonably practicable;
 11. MTA and its engineering consultants have expertise11. MTA and its engineering consultants have expertise
designing and building tunnels and subway stations in Losdesigning and building tunnels and subway stations in Los
Angeles; andAngeles; and
 12. The Constellation Station will attract more riders than12. The Constellation Station will attract more riders than
the station locations along Santa Monica Boulevard.the station locations along Santa Monica Boulevard.

19. In Recent NewsIn Recent News
 As of late 2014 Beverly Hills is stillAs of late 2014 Beverly Hills is still
trying to appeal the decision totrying to appeal the decision to
tunnel under BHHS, recruitingtunnel under BHHS, recruiting
students to make anti metro subwaystudents to make anti metro subway
films...films...
 The current ruling still stands andThe current ruling still stands and
plans have been made to bore underplans have been made to bore under
the high school.the high school.

20. Possible Routs Through Century CityPossible Routs Through Century City

22. SourcesSources
 http://www.metro.net/projects/westside/http://www.metro.net/projects/westside/
#constructionimpacts#constructionimpacts
 http://thesource.metro.net/2011/10/19/ehttp://thesource.metro.net/2011/10/19/e
xperts-speak-to-metro-board-about-xperts-speak-to-metro-board-about-
westside-subway-extension-seismic-westside-subway-extension-seismic-
issues-in-century-city-a-constellation-issues-in-century-city-a-constellation-
station-is-recommended/station-is-recommended/
 http://media.metro.net/board/Items/2012/05http://media.metro.net/board/Items/2012/05_